This invention relates to a torque limiting device and, more particularly, to a gear having a torque limiting, radial friction clutch. Speed-reducing gear trains include gear combinations comprising a relatively large gear and an integral, axially projecting pinion gear for reducing rotational speed and increasing torque through the gear train.
A wide variety of gear mechanism exist which receive input power from prime movers such as hydraulic or electric motors and multiply the torque output of the motor as a function of speed reduction for a desired high torque or slow speed output through the gear mechanism or train. For example, speed reducing mechanism sin the form of gear trains are employed in appliance timers wherein high-running torque synchronous motors are employed to drive the drum or disk-shaped timer cam which, in turn, sequentially actuates an array of leaf spring switch arms to electrically control the various functions of the appliance. Since the timer cam must be rotated at a relatively low speed to accomplish a variety of switching operations in one revolution, the gear train must greatly reduce the rotation speed of the motor. If a restraint is placed on the cam by a foreign object or a defective switch arm while it is driven, the normal operational torque of the gear train is greatly increased to a point where the gear teeth on one or more gears may be stripped. This is particularly true in those applications which employ plastic gears. Since the gears are assembled as a package with the motor, it is necessary to replace the entire gear train and motor assembly, or in many cases, the entire appliance timer, if a single gear should become stripped.
Many other mechanisms employing clock-type gear drives encounter similar problems where unexpected blockages are encountered by the power output of the gear train causing gear tooth stripping or dislodgement of a gear from its mounting shaft. Moreover, the output of the gear train may be manipulated to force the gears into an abnormally high torque load condition such as by, for example, moving the hands of a clock timing-device manually.